A stereotactic brain implant technique with high activity I-125 seeds using a conventional brachytherapy treatment...

A stereotactic brain implant program with removable high-activity I-125 seeds has recently been implemented for the treatment of malignant brain tumors. A Brown-Roberts-Wells (BRW) stereotactic frame with an NIH arc system and a guide template is used to introduce parallel catheters precisely into the tumor volume (Fig. 1). CT scans of patients with the BRW frame in place are used to determine the position of the catheters and the location of seeds in each catheter. The positions of the catheters are determined with respect to a "reference line" which represents the direction of approach in the central plane of the tumor. The seed coordinates are expressed in the catheter coordinate system with the X-axis along the catheter direction and the Y-Z plane parallel to the surface of the guide block. The Y-Z plane is orthogonal to x-axis. An AECL Theratronics Theraplane treatment planning system (SEED program) is used to obtain dose distributions based on seed coordinates. This treatment planning system does not require special purpose software for brachytherapy treatment planning. High-activity I-125 seeds (nominal 10-15 mCi/seed) are after-loaded into the inner catheters of double coaxial silicone (Gutin) catheters according to a preplanned scheme. The physical aspects of the brain implant program, treatment planning technique, and radiation safety measures are described.